Method of obtaining evidence of traffic signal violations



F. ABELL Jan. 27, 1959 METHOD OF OBTAINING EVIDENCE OF TRAFFIC SIGNAL VIOLATIONS Filed Oct. 18, 1952 2 Sheets-Sheet 1 INVEN TOR. CZ Za/nk m WIILHW.

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United States Patent METHOD OF OBTAINING EVEDENCE OF TRAFFIC SIGNAL VIOLATIONS Frank Abell, Inglewood, Calif.

Application October 18, 1952, Serial No. 315,552

11 Claims. (Cl. 3461) This invention relates to methods for obtaining evidence of trafiic violations, with special reference to violations of automatic traflic signals at intersections, and is directed specifically to a method of obtaining conclusive photographic evidence of such violations. This application is a continuation-in-part of my copending application entitled Means and Method of Obtaining Evidence of Trafiic Signal Violations, Ser. No. 644,514, filed lanuary 31, 1946, now abandoned.

In citing autoists for trafiic violations it is desirable to provide convincing evidence not only for the purpose of proving a violation in the face of a possible denial but also for the sake of removing from the mind of the accused any doubt he may have of the fairness of the police officer in making the charge. The general object of the present invention, therefore, is to provide a simple and inexpensive method for producing incontrovertible photographic evidence of trafiic violations at a signalcontrolled intersection.

Attempts have been made to use motion picture cameras to obtain such evidence but to my knowledge no practical procedure has been suggested for obtaining motion picture evidence that is both economical in film and capable of linking the trafiic violation with the cycle of operation of the trafiic signal. It is not enough to produce a photograph of a vehicle in motion in the intersection zone; adequate evidence of a trafiic violation requires positive proof that the photograph Was taken at a moment when trafific in the direction of the vehicle was barred by the traflic signal.

The invention is based on the fact that if the operating cycle of a trafiic signal is known, i. e., if the duration of the stop period and the. go period of the cycle are known, and if the synchronism. of the operating cycle with local time is known,. a traific violationat the intersectionby a vehicle during the stop period of the signal may be proved by two successive photographs of the violating vehicle at known moments. of local time. Thus if it is known that a traffic signal operates with stop and go periods of twenty seconds each and if it is further known that on a given day the signal changed at 48 minutes and 16.4 seconds after 3:00 p. m., the stop and go periods of the signal cycle can be defined in terms of local time and the movements of the vehicle in the intersection in relation to the signal cycle may be proved lay-photographing the violating vehicle and including in the photograph a time piece or time indicator to show local time.

At least the duration of the stop period of the cycle of operation of the traffic signal must be known in all practices of the invention and the duration of both the stop period andthe go? period must be known in some of the practices. The operating cycle ofv the trafiic signal and the synchronism of the operating cycle with respect to local time may be. determined by various nonphotographic proceduresif desired. One object of the invention, however, istoprovide: a simpletphotographic method of determining the cycle of operation of a trafiic signal in terms of local time.

A further object of the invention is to provide a method of photographic proof of violations that may be used either for traffic moving in the general direction in which the camera is pointed or for cross trafiic transverse to the direction in which the camera is trained.

One of the practices of the invention has for its object the proof of a signal violation with a minimum number of photographs and without the necessity of determining the exact synchronism of the signal with respect to local time. In this procedure two successive photographs of the vehicle, including both a clock and a trafiic signal together with the vehicle, prove that the vehicle is in motion in the intersection during a stop period of the signal and a third photograph establishes the approximate synchronism of the signal with respect to local time in such manner that the margin of possible error in the approximation favors the violator. Thus only three photographs are required in this procedure.

In a second practice of the invention, synchronism of the signal cycle with local time is established with greater precision to permit the cycle of operation of the signal to be plotted with relatively close accuracy in terms of local time. A feature of this second practice of the invention is that it avoids the necessity of including the trafiic signal in the two pictures that are taken to prove that the vehicle is in motion in the intersection zone.

The various objects, features and advantages of the invention may be understood from the following description in conjunction with the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative, Fig. l is a diagrammatic sectional view of a motion picture camera that may be used for practicing the invention;

Fig. 2 is a diagrammatic plan view of the optical system incorporated in the camera to photograph a time mechanism or watch;

Fig. 3 is a representation of three photographs to prove a trafiic violation in one practice of the invention;

Fig. 4 is arepresentation of four photographs to prove a trafiic violation in a second practice of the invention;

Fig. 5 is a diagram illustrating how a series of photographs may be utilized to establish the duration of both periods of the cycle of operation of a traific signal and to establish the synchronism of the cycle with respect to local time;

Fig. 6 is a diagrammatic view explaining how the three photographs of Fig. 3'prove a trafiic violation; and

Fig. 7 is a similar diagrammatic view explaining how the four photographs of Fig. 4 prove a traffic violation.

In Fig. l, which shows a motion picture camera which may be used to take one frame at a time in-the practice of the invention, the film guide is designated 11, the camera shutter 12, the main lens 13, and the photographic film 14. This camera is shown more specifically in Fig. 2 as havingan auxiliary lens 15 which, through a prism 16, reflects-the image of the face of the time piece or watch 17 on the 'film 14. As shown in Fig, 1, there is provided an auxiliary shutter 18 for controlling the projection of the image of the watch face on the film. Insteadof such shutter, a switch (not shown) may be provided in the circuit (not shown) for the Watch-illuminating'bulbs 19.

in operation, when the camera motor (not shown) is released, shutters 12 and i3 uncover the portion of the film M in the film guide 12 to the images in front of the lenses l3 and 15, respectively, exposing the film simultaneously. The time mechanism or watch 17 may have an hour face with a sweep second hand so that it may be easily photographed to show seconds and decimal portions of seconds. i 7

It is to be understood that the invention may be practiced with other camera constructions. For example the camera construction may be such as disclosed in my prior Patent 2,250,442 entitled Speed Recording Method and Device issued July 29, 1941, which prior patent is hereby made a part of the present disclosure by reference. It is also to be understood that it is not necessary to incorporate a time piece in the camera to prove the time at which a picture is taken since the same proof may be obtained by photographing a time piece or clock outside of the camera.

The cycle of operation of an automatic traffic signal comprises a stop period during which trafiic is barred by the signal with respect to movement in one direction across the intersection and a go period in which traffic movement is permitted in the given direction. Traffic signals are commonly adjusted with respect to the duration of the stop and go periods in accord with the tratfic at a particular intersection and usually operate without change in the cycle over a relatively long period of time. Thus, if the cycle of operation of a tramc signal is determined at a given hour on a given date, it may be assumed for the purpose/of proving a trafiic violation that the operation of the traffic signal on the determined cycle was continuous over a period of minutes and even hours before and after the given hour. Typical operating cycles in terms of seconds for the stop and go periods are 20-20, 30-30, 70-70, 35-25, 40-20, etc.

For the purpose of the present invention the cycle of operation for which a trafiic signal is adjusted to operate may be proved in various ways. Automatic means may be operatively connected to the traflic signal to record the operating cycle; or a time study supported by an affidavit may establish the operating cycle and how it synchronizes with local time. A feature of the present invention, however, is that the police ofiicer using the described camera to photograph a vehicle for the purpose of proving a traffic violation may use the same camera to ascertain and prove the time sequence of the operating cycle of the tralfic signal as well as the relation of the operating cycle to local time. How the camera may be used for this purpose may be understood by referring to photographs (c) and (d) of Fig. 4 and by further referring to Fig. 5.

Fig. shows a record sheet 24 on which'is printed a series of marks to form a graduated time scale 25. Each graduation of the time scale 25 may be taken to represent, for example, two seconds so that every five lines of the scale represent ten seconds. It is not necessary to provide and use such a printed scale to carry out the invention, as will be apparent, but such a scale is used in the preferred practice of the invention to simplify the procedure of arriving at the operating cycle of a trafiic signal as Well as to simplify the task of showing in court how a set of photographs completely establish the operating cycle of a trafiic signal.

For the purpose of proving the adjustment of a given traflic signal with respect to its operating cycle and with reference to local time a time scale such as the time scale 25 or its equivalent is .used in conjunction w h successive pairs of photographs such as the photographs (0) and (d) of Fig. 4.

Photograph (0) is taken close to the end of a go period of the cycle operation of a traffic signal 'Zdwhile the traffic signal still shows a green light 27 and photograph 4(d) is taken immediately after the traflic signal changes to show a red light 28. It is a simple matter to check the duration of the go" and stop period of the traffic signal and then with the aid of a stop watch to anticipate the moment of signal change to make the two photographs 4(0) and 4(d) close to the point in time at 2,s71,oss- 4 which the signal changes. The image 30 in photograph 4(c) of the watch 17 in the camera shows the local time immediately before the signal change and the image 31 in photograph 4(d) shows the time just after the signal change. Thus the two photographs bracket a short period of time, for example, a time period on the order of magnitude of one second, during which the signal change from green to red.

The time notations shown in Fig. 5 are taken from three pairs of photographs (not shown) like the pair of photographs 4(0) and 4(d), the six photographs being taken in the following sequence with the following time indications shown by the diiferent photographic watch images. A photograph taken at 12:50:09.2 shows the signal indicating green or go and a photograph taken at 12:58:19.4 shows the traffic signal indicating red or stop, the pair of photographs indicating that the signal changed from go to stop during the intervening interval of 1.2 seconds. A second pair of pictures show the traffic signal indicating red or stop at 12:50:39 and indicating green or go at 12:50:40.2 to establish the fact that the signal changed from stop to go in the intervening time interval of 1.2 seconds. Thus the four time notations from four corresponding photographs show that the traffic signal is operating with a stop period of approximately 30 seconds.

in some instances the only information about the traffic signal operating cycle required to prove a traflic violation is the duration of the stop period of the cycle. In other instances, as will be explained, the duration of the go period must also be obtained to provide complete information about the operating cycle of the signal. For this purpose Fig. 5 shows notations for a third pair of photographs as follows: the traflic signal indicated green or go at 12:51:09.2 and red or stop at 12:51:10.6, thus proving that the traflic signal changed from go to stop in the intervening time interval of 1.4 seconds. Since the time duration of either period of the signal cycle can be assumed to be a multiple of 5 seconds, the six photographs prove that the signal is operating on a 30-30 cycle and in addition establish the synchronism of the trafiic signal operating cycle relative to the indicated time, i. e., local time within a margin of error of 1.2 seconds.

For convenience in computing and proving traflic violations the invention preferably further contemplates the provision of a number of different cycle scales for use with a time scale such as time scale 25, there being one such cycle scale for each of common operating cycles for which traffic signals are adjusted. Such a cycle scale, as shown fragmentarily in Fig. 5, may comprise, for example, a suitable strip 33 of metal or plastic material on the margin of which is a series of alternate green bars 34 and red bars 35 representing the go" and stop periods r of the operating cycle of a traffic signal. The particular cycle scale designated 33 in Fig. 5 represents a 30-30 signal operating cycle. It is apparent that when the cycle scale 33 is positioned adjacent the time scale 25 to match thetime notations thereon that are taken from the six successive photographs it is established beyond any doubt that the 30-30 cycle is the correct cycle.

It is to be understood of course that neither the time scale 25 nor the cycle scale 33 is necessary to define the operating cycle of the traflic signal and to show the synchronism of the operating cycle relative to local time, since the six time notations in Fig. 5 speak for themselves. The use of the time scale and the cycle scale, however, saves mental. computation and puts the proof in convenient visible form to simplify greatly the necessary explanation of how the three pairs of photographs serve their purpose of completely defining the operating cycle of the traflic signal.

It is also to be understood that in all the practices of the invention where'the operating cycle and the synchronism of the operating cycle of the traffic signal relative to local time must be established to prove a traffic violation, the necessary proof of the operating cycle and its synchronism relative to local time may be derived from automatic recording devices, affidavits of qualified observers, etc.

Fig. 3 illustrates how three photographs may 'be used to prove a traffic violation on the part of a vehicle moving into an intersection zone from a direction transverse to the direction in which the camera is pointed. The line 38 in the image of the three photographs (a), (b) and (c) is a painted line commonly placed in the middle of the highway and serves as a reference for arriving at the approximate position of a vehicle relative to the intersection area. The vehicle image 39 in photograph 3(a) proves that the vehicle was in the intersection area and the vehicle image 40 in photograph 3(1)) shows that the vehicle was in a more advanced position a short time later thereby proving that the vehicle was in motion in the intervening time period. The watch image 41 in photograph 3(a) and the watch image 42 in photograph 3(1)) show the local time of the two successive photographs to be respectively 2:37:29.8 and 2:37:30.6 so that the intervening time period is 0.8 second. In both photographs 3(a) and 3(b) the trafiic signal image 45 shows a green light 46 and therefore proves that the traffic signal indicated stop for the direction of cross traffic in which the vehicle in the two photographs is moving.

The operator of the camera taking the pictures 3(a) and 3(b) waits until the immediately next change in the traihc signal and then as promptly as possible takes the third photograph 3(a). in the picture 3(0) the traffic signal image 45. shows .a red light 47 thus showing that the signal has changed to green or go for the transverse direction of travel of the violating vehicle. The time indicated by the watch image 48 in picture 3(a) is 2:37:55.2 I

The time data obtained by the three photographs of Fig. 3. may be handled mentally or may be placed in some convenient tabular form to prove that the photographed vehicle violated the trafiic signal; but here again a feature of the invention is the convenience and simplicity of a preferred procedure involving the use of a graduated time scale together with an appropriate cycle scale. Fig. 6 illustrates how these accessories clearly and: graphically prove the traffic violation represented by the three photographs in Fig. 3.

Fig. 6 shows a record sheet 24 with a time scale printed thereon as heretofore described. At any convenient point on the time scale 25 the police otficer makes the first notation 2:37:29.8 taken from photograph 3(a) and then makes the other two notations representing photographs 3(1)) and 3(c) at the proper positions on the time scale relative to the position of the first notation. It is assumed that it has already been established beyond doubt that the trafiic signal is operating on a 30 cycle. It is merely necessary, therefore, to place the 3030 cycle scale in the position shown in Fig. 6 to prove that the vehicle violated the traffic signal.

In Fig. 6 the cycle scale 33 is placed with a red bar extending over the region of the first two time notations and as close as possible to the third time notation 2:37:55.2 but not quite at this third time notation since the third photograph 3(0) is taken during the go period of the trafiic signal for the direction in which the violating vehicle is moving. It is to be especially noted that the actual synchronization of the operating cycle of the traffie signal with respect to local time or the time shown by the watch in the camera does not enter into the proof of the violation. The described position of the cycle scale 33 relative to the three time notations is a deduced approximate position for the cycle scale representing a deduced approximate synchronization of the operating cycle relative to the time indicated by the watch. From this. deduced synchronism of the operating cycle it appears that the traffic signal had been. indicating stop,

in the direction of travel of the vehicle for at least 5 seconds prior to the taking of picture 3(a). The 5 second time interval is minimum because any error in approximation of the deduced position of the cycle scale 33 is in favor of the violating vehicle rather than in favor of the police otficer who is using this technique to prove the violation.

The 5 second margin of violation of the stop period of the trafiic signal indicated by the position of the cycle scale 33 in Fig. 6 is a minimum margin because the third photograph 3(0) is taken with time delay after the end of the stop period of the traffic signal cycle. If, for example, after the signal changes to green for the direction-of the vehicle there is a relatively long delay on the order of 4 seconds before the third photograph 3(0) is taken, the actual synchronization of the tratfic signal operating cycle relative to the time shown by the watch i. e. the accurate position for the cycle scale 33 will be the position shown at 33a in Fig. 6. At this second accurate position of the cycle scale it is apparent that the traffic signal chan ed to stop forthe violating vehicle a full 9 seconds before the first photograph 3(a) was taken and therefore the deduced position for the cycle scale compared to the accurate position favors the violator by a margin on the order of 4 seconds in this particular instance. Since any errors of approximation always favor the violating vehicle in this manner the approximation procedure provides incontrovertible evidence of a trafiic violation.

It is to be noted that the foregoing proof of a trafiic violation represented by Fig. 6 requires merely the duration of the stop period of the trafi'ic signal cycle. It is possible therefore to prove a tratlic violation in this way by merely establishing the duration of the stop period Without going so far as to define and prove the whole operating cycle.

An important feature of the practice of the invention exemplified by Figs. 3 and 6 is that the two photographs 3 and 3(1)) may be used to prove the approximate speed of the vehicle. In some instances the two photographs also prove whether the vehicle is accelerating or decelerating between the two photographed positions since there is a limit as to how far a vehicle can advance from a standing start in such a short period of time.

When the two photographs 3(a) and 3(b) are combined with photograph 3(0), moreover, the approximate distance of the vehicle-from the traific signal when the traflic signal changed to stop may be deduced. Thus if the first two photographs taken together indicate that the vehicle was moving at a given number of feet per second and the traffic signal changed to stop 5 seconds before the first picture was taken the vehicle was at least 5 times the given number of feet back of the first photographed position when the signal changed. Here again the described approximation method favors the violatingvehicle since establishing the actual synchronization of the traffic signal cycle relative to local time would prove the vehicle to be even further from the signal when the signal changed.

The described method of proof of a trafi'ic violation exemplified by Figs. 3 and 6 is also applicable tothe proof of a traific violation by a vehicle in cross trafiic at an intersection Where the traflic signal operates in response to arrival of a cross traflic vehicle at the intersection. On highways in thinly settled areas it is common practice to install a trafiic signal that indicates go for the main highway trafiic so long as no vehicle approaches the intersection in a cross tratfic direction. When such a cross traitic vehicle approaches the intersection, suitable provision is made for the vehicle to trigger the traffic signal and cause the traffic signal to change from stop to go for the cross trafiic vehicle for a predetermined time period, say a period of 30 seconds or less. that a traffic ofiicer may establish the duration of the cross trafiic go of such a signal for use if necessary to It is apparent 7 prove a traffic violation; and it will be readily understood how with such signal cycle data, a series of photographs such as the photographs in Fig. 3 may be used to prove a violation by a cross traffic vehicle.

In the procedure discussed above the direction of traffic is transverse to the direction in which the camera is pointed and the procedure is characterized by the inclusion of a traffic signal in the two photographs that prove the vehicle to be in motion. Fig. 4 exemplifies a second procedure in which the two photographs to prove the vehicle is in motion are taken with the vehicle moving in the direction in which the camera is pointed. Fig. 4 also is an example of a practice of the invention in which no trafiic signal appears in the two photographs of the violating vehicle. Fig. 4 further exemplifies a practice of the invention in which the license number of the vehicle appears in the photograph to remove any possible doubt about the identity of the vehicle.

The photograph 4(a) has an image 53 of a vehicle in the intersection zone with the license number 54 of the vehicle clearly legible and the image 55 of the camera It is apparent that if the cycle of operation of the traffic signal at the intersection and the synchronism of the cycle of operation with respect to the indicated time are known and proved, it is a simple matter to prove that the vehicle in photographs 4(a) and 4(b) is violating a signal. It is merely necessary, for example, to make notations on a time scale corresponding to the two photographs and to apply a cycle scale to the time scale. The cycle scale corresponds to the cycle of operation of the traffic signal and is placed in relation to the time scale in accord with the synchronism of the operating cycle with respect to local time.

The question may arise however as to whether or not the synchronism of the operating cycle relative to local time has shifted for any reason and it is advisable, therefore, to provide a photographic check on the synchronism either before or shortly after the traffic violation. The two photographs 4(a) and 4(d) are taken for this purpose.

The two photographs 4(0) and 4(d) are taken at the same intersection but the camera position is shifted to include the traific signal in the image. The fact that the traffic signal is located at the particular intersection in which the violation occurred is proved by including in the photographs 4(a) and 4(d) an image 60 of the same building as represented by images 58 in photographs 4(a) and 4(1)). The photograph 4(0) shows the traflic signal indicating green or go at 12:41:55 and photograph 4(d) shows the traflic signal indicating red or stop at 12:41 :5 6.2. Thus the moment at which the traflic signal changed in its cycle of operation is bracketed as falling within a time interval of 1.2 seconds. Since the traflic signal is known to operate on a 30-30 cycle, the trafiic violation may be proved by calculation, preferably by means of a time scale and cycle scale as shown in Fig. 7.

In Fig. 7 the time scale 25 is taken as representing two seconds per graduation and time notations corresponding to the four photographs of Fig. 4 are made on the time scale in correct spacial relations in accord with their relations. Since the two photographs 4(0) and 4(d) bracket a point in time at which the signal changed from go to stop, the cycle scale 33 in Fig. 7 is positioned accordingly relative to the time scale with the result that the two time notations corresponding to Figs. 4(a) and 4(b) fall well within the time interval represented by a 8 red or stop block 35 of the cycle scale to prove the trafiic violation. While in this example pictures 4(a) and 4(d) are taken to show a signal change from go to stop, it is apparent that two similar pictures showing a signal change from stop to go will serve the same purpose.

It is apparent that a traihc officer working alone can carry out the described photographic procedure and in addition may serve traffic citations on the violating motorists. A feature of the invention, however, is that it lends itself to a procedure in which more than one ofiicer work together as a coordinated team. For example, one traffic ofiicer sitting in a car at an intersection may take a set of photographs of a violating car and radio instructions to one or more trafiic ofiicers at remote points to issue citations to the violators.

In all the foregoing examples it has been assumed that the traffic signal does not have a warning light that lights up just before a signal change. It will be readily apparent, however, that merely photographing the signal in the described manner with the warning light illuminated in the photograph will approximately determine the time of signal change.

My detailed description of preferred practices of the invention by way of example will suggest to those skilled in the art various changes, substitutions and other departures from my disclosure that properly lie within the spirit and scope of the appended claims.

I claim:

1. The method of producing photographic evidence of a trafiic violation by a moving vehicle at an intersection equipped with an automatic traiiic signal operating with a cycle of stop and go periods of known duration, which method includes the steps of: photographing a time indicator synchronized with local time together with the vehicle at two successive moments in time to show the vehicle in two successive positions in the intersection during a single stop period of the signal cycle; and photographing a time indicator synchronized with local time together with said traflic signal at least once immediately after the end of said stop period to establish the time relation between the traflic violation and the operating cycle of the traffic signal thereby to prove the two successive positions of the vehicle as occuring in the stop period of the signal.

2. The method as set forth in claim 1 in which the license plate of the vehicle is included in the photograph to prove the identity of the vehicle.

3. The method of producing photographic evidence of a tratlic violation by a moving vehicle at an intersection equipped with an automatic trafiic signal which includes the steps of: recording the changes of said trafiic signal to establish the duration of at least the stop period of the operating cycle of the signal; photographing a time indicator synchronized with local time together with the traific signal and the vehicle at one moment and again at a latter moment during a single stop period to show the vehicle in two successive positions in the intersec tion during said single stop period of the traffic sign-a1; and photographing the tralfic signal together with a time indicator synchronized with local time after the immediately next change of the signal to go.

4. The method of producing photographic evidence of a traflic violation by a moving vehicle at an intersection equipped with an automatic trailic signal, which includes the steps of; recording the changes of said trafiic signal to establish the duration of the stop and go periods of the cycle of operation of the signal and to establish the synchronism of the cycle of operation with respect to local time; and photographing a violating vehicle together with a local time indicator synchronized with local time at two successive moments during a single stop period to prove the vehicle to be in motion in the intersection between said two moments whereby the traflic violation may be proved by the cycle of operation of the signal.

5. The method of producing photographic evidence of 1 a traflic violation by a moving vehicle at an intersection equipped with an automatic trafiic signal operating with a cycle of stop and go periods of known duration, which method includes the steps of: photographing a time indicator synchronized with local time together with a vehiclt in the intersection at two successive moments in time during a single stop period to show the vehicle in two successive positions in the intersection; and photographing the trafiic signal together with a time indicator synchronized with local time immediately before and immediately after a signal change to estblish the synchronism of the operating cycle of the signal with respect to indicated time thereby to prove that the two successive pictures of the vehicle were taken during a stop period of the operating cycle.

6. The method of producing photographic evidence of a trafiic violation by a moving vehicle at an intersection equipped with an automatic traflic signal, which includes the steps of: photographing the traffic signal together with a time indicator synchronized with local time at different times of change of the traflic signal to establish the duration of the difierent periods of the cycle of operation of the traflic signal and to establish the synchronization of the cycle of operation relative to the indicated time; and photographing a time indicator synchronized with local time together with the vehicle at two successive moments in time during a single stop period to show the vehicle in two successive positions in the intersection whereby the two photographs showing the vehicle to be in motion may be correlated with the operating cycle of the signal to prove the traflic violation by the vehicle.

7. A method as set forth in claim 6 in which the recording of. the changes of the traflic signal is carried out by photographing the tramc signal together with a time indicator synchonized with local time immediately before and immediately after a time of change of the traffic signal.

8. The method of producing photographic evidence of a tratfic violation by a moving vehicle at an intersection equipped with an automatic traflic signal operating with a cycle of stop and go periods of known duration, which method includes the steps of: photographing a vehicle together with a time indicator synchronized with local time at two successive moments during a single stop period to show the vehicle in two successive positions in the intersection; photographing the trafiic signal together with a time indicator synchronized with local time at least once to establish the synchronism of the operating cycle of the signal with respect to the indicated time; plotting time notations 011 a time scale in accord with the photographed time indications; and applying to said time scale a cycle scale representing the cycle of operation of the trafiic signal to prove the two photographs of the vehicle in motion weretaken during a stop period of the cycle of operation of the tratfic signal.

9. A method as set forth in claim 8 in which synchronization of the operating cycle of the traffic signal with respect to the indicated time is established by photographing the trafiic signal together with a time indicator synchronized with local time immediately after the traflic signal changes.

10. A method as set forth in claim 8 in which the synchronization of the cycle of operation of the trafiic signal relative to the indicated time is established by photographing the traflic signal together with a time indicator synchronized with local time both immediately before and immediately after the signal change.

11. The method of producing photographic evidence of a traffic violation by a moving vehicle at an intersection equipped with an automatic traffic signal operating with a cycle of stop and go periods of known duration, which method includes the steps of: photographing a vehicle together with a time indicator synchronized with local time at two successive moments in time during a single stop period to show the vehicle in two successive positions in the intersection; photographing the tratlic signal with a time indicator synchronized with local time at least once to establish the synchronism of the operating cycle of the trafiic signal relative to the indicated time; plotting the time indications revealed in the resulting photographs; and plotting the cycle of operation of the signal over a period of time including the period of time in which the photographs were taken to prove that the two photographs of the vehicle in motion were taken during a single stop period of the cycle of operation of the trafiic signal.

References Cited in the file of this patent UNITED STATES PATENTS 2,232,829 Ross Feb. 25, 1941 2,347,194 I-Iolliday Apr. 25, 1944 2,349,355 Kepler May 23, 1944 2,619,402 McCutcheon Nov. 25, 1952 2,683,071 Pearle July 6, 1954 

